THE QUESTION What drives us to be charitable to strangers when it is costly to ourselves? Researchers investigated the role that the hormone oxytocin plays in regulating our generous behavior.

THE METHOD Produced naturally during sexual arousal and childbirth, oxytocin has long been linked to social behaviors. By binding to brain regions associated with emotion, the hormone helps parents bond with children and increases trust. Adding a twist to this story, neuroeconomist Paul Zak of Claremont Graduate University proposed that oxytocin might also play a role in material generosity by promoting the ability to empathize with others.

To test his hypothesis, Zak focused on monetary transfers. He rounded up 68 male participants (women were excluded because oxytocin increases the risk of miscarriage) and administered oxytocin to half of them through a nasal inhaler. The other half inhaled only salt water. Then participants were paired randomly and identified only by a number via computer, a setup that prevented them from identifying each other or talking at all.

In a first round of trials, subjects were told that one of each pair would receive $10 but would need to offer his partner a share. If the partner accepted the offer, they would divide the money as proposed by the other partner. But if the subject rejected the offer—which might happen if the offer seemed too stingy—neither person would get anything. Prior to learning which role he would assume (giver or receiver), each participant was asked to decide on personal courses of action—if doling out the money, how much would he give, and if receiving, what was the minimum offer he would accept? “We used this strategy to force people to take another’s perspective,” Zak explains. The money was real, and players received cash at the end in accordance with these rules.

In a second round, the same people were paired, but this time the receiving partner had no say over the offer: He had to accept it, no matter what it was.

THE RESULTS In the first part of the study, oxytocin made no difference whatsoever in the minimum offer a partner was willing to accept: It was $2.97, on average, regardless of whether he received the hormone or a placebo.

But when it came to the actual generosity of giving, oxytocin mattered a lot. Those inhaling the hormone offered an average of $4.86 compared with $4.03 for those who inhaled saline. In fact, those who received oxytocin were so giving that they actually left the lab with about 5 percent less money than their placebo counterparts.

Results were different in the second trial, where recipients had to accept the offer no matter what. With no possibility of rejection, offers were lower overall ($3.68 on average), and there was no statistical difference between the oxytocin and placebo groups. In other words, oxytocin had no effect.

THE MEANING Since oxytocin increased the level of giving only in the first transaction—in which the partner’s response mattered—Zak concludes that the hormone’s effect is specific, altering generosity only when we have to think about others’ feelings. “When something drives us emotionally, when we feel connected to other people, that’s when we open our wallets,” he says.

Should you worry about casinos or charities spritzing this stuff in the air to make you spend or give more? “The answer is no,” Zak says. “You have to get a lot in your nose to get it into your brain. You would know you were getting it up your nose.” The larger danger is manipulation of our empathy and generosity through heart-wrenching images or narratives that cause the natural release of oxytocin to the brain.

Part of the motivation behind investigations like this one, Zak says, is that “as we become aware of these unconscious processes, we have better control over them.” But we would not want to override oxytocin’s effects. By increasing empathy, he says, oxytocin “makes us bind together as a species. All kinds of daily transactions require that people spend just a little bit of their time and resources to help someone out. I think society as we know it couldn’t exist without that.”

Stats Behind the study
• Donors in the United States gave $295 billion to charities
in 2006.
• Nearly $223 billion of that came from individuals.
• Who got the money? A third went to religious congregations, and 14 percent went to education. Foundations and human services organizations received more than 10 percent each. Cultural organizations and international affairs groups received 4 percent each.
• The average person in the United States gave away 2.2 percent of after-tax income in 2005.
• That same year, 65 million Americans donated time to charities.
• 96 percent of volunteers said “feeling compassion toward other people” motivated them to give their time.
• Previous research by Zak and his colleagues suggests that because estrogen increases the number of oxytocin receptors, in countries where people consume larger amounts of plant-based estrogens (found in foods such as nuts, soy products, and legumes), average trust levels are higher.